Sheet-type cell and method for manufacturing same

ABSTRACT

A sheet-type cell disclosed in this application includes an outer case and a power generation element contained in the outer case. The power generation element includes a positive electrode, a negative electrode, a separator, and an electrolyte solution. The separator is constituted by a porous resin sheet. The outer case includes a first outer case member and a second outer case member. Each outer case member includes a thermally fusible resin layer. The first outer case member and the second outer case member are disposed on respective opposite sides of the power generation element. A periphery of the first outer case member and a periphery of the second outer case member are sealed by thermally welding, with a periphery of the separator interposed between the peripheries of the first and second outer case members.

TECHNICAL FIELD

The present application relates to a sheet-type cell excellent inproductivity and a method for manufacturing the same.

BACKGROUND ART

An air cell includes a positive electrode and a negative electrode. Thepositive electrode is formed of an air electrode including a catalystsuch as manganese dioxide or carbon. The negative electrode includesmetal particles such as zinc-based particles, e.g., zinc particles andzinc alloy particles, as an active material. Such an air cell has beenused for many years as a power supply for. e.g., a hearing aid.

This type of cell has been generally in the form of a button cell withan outer case made of a metal can, but a sheet-type cell has beendeveloped in recent years. For example, in the sheet-type cell, an outercase is formed of aluminum laminated films used as outer case members,and a periphery of one of the outer case members proximate to a positiveelectrode and a periphery of the other outer case member proximate to anegative electrode are thermally welded to each other to be sealeddirectly (e.g., Patent Document 1).

PRIOR ART DOCUMENT

-   Patent Document-   Patent Document 1 JP6454824 B (see e.g., Examples)

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

Meanwhile, usually, a positive electrode terminal and a negativeelectrode terminal are drawn from both peripheries of outer case membersin such a sheet-type cell. The electrode terminals are interposed in athermally welded portion between the peripheries of the outer casemembers, thereby causing poor sealing properties therebetween. Thus, forexample, a step of further interposing an ionomer film between theperipheries in an area where the electrode terminals are present isrequired. In the case of a non-aqueous electrolyte solution cell,intrusion of moisture into the cell through a thermally welded portionof an outer case is an issue. Thus, it is required to form the thermallywelded portion as thin as possible, and it is desirable to interpose asfew components as possible other than the outer case in the thermallywelded portion between peripheries of outer case members.

Meanwhile, in order to improve the productivity of sheet-type cells,production of sheet-type cells by a roll-to-roll method has beenconsidered. However, in a method of placing the entire positiveelectrode, negative electrode, and separator in a space within an outercase, when the sizes of the positive electrode and the negativeelectrode are set to be as large as possible in order to obtain asufficient capacity, there is no difference in the sizes of the positiveelectrode, the negative electrode, and the separator, and the accuracyof positioning of the separator is needed to be improved. This resultsin a reduction in the productivity.

This application has been made in view of the circumstances as describedabove, and provides a sheet-type cell excellent in productivity and amethod for manufacturing the same.

Means for Solving Problem

A sheet-type cell disclosed in this application includes an outer caseand a power generation element contained in the outer case. The powergeneration element includes a positive electrode, a negative electrode,a separator, and an electrolyte solution. The separator is constitutedby a porous resin sheet. The outer case includes a first outer casemember and a second outer case member. Each outer case member includes athermally fusible resin layer. The first outer case member and thesecond outer case member are disposed on respective opposite sides ofthe power generation element. A periphery of the first outer case memberand a periphery of the second outer case member are sealed by thermallywelding, with a periphery of the separator interposed between theperipheries of the first and second outer case members.

A method for manufacturing a sheet-type cell disclosed in thisapplication is a method for manufacturing a sheet-type cell including anouter case and a power generation element contained in the outer case.The power generation element includes a positive electrode, a negativeelectrode, a separator, and an electrolyte solution. The separator isconstituted by a porous resin sheet. The outer case includes a firstouter case member and a second outer case member. Each outer case memberincludes a thermally fusible resin layer. The method includes disposingthe first outer case member and the second outer case member onrespective opposite sides of the power generation element, and thermallywelding to seal the first and second outer case members disposed on therespective opposite sides of the power generation element and theseparator in a state where an outer portion of the separator facingneither the positive electrode nor the negative electrode is interposedbetween a periphery of the first outer case member and a periphery ofthe second outer case member.

Another aspect of the method for manufacturing a sheet-type celldisclosed in this application is a method for manufacturing a sheet-typecell including: an outer case; and a power generation element and awater repellent membrane that are contained in the outer case. The powergeneration element includes a positive electrode, a negative electrode,a separator, and an electrolyte solution. The water repellent membraneis disposed between the outer case and the positive electrode. Theseparator is constituted by a porous resin sheet. The outer caseincludes a first outer case member and a second outer case member. Eachouter case member includes a thermally fusible resin layer. The methodincludes disposing the first outer case member and the second outer casemember on respective opposite sides of the power generation elementprovided with the water repellent membrane on an outer surface of thepositive electrode in the power generation element, and thermallywelding to seal the first and second outer case members disposed on therespective opposite sides of the power generation element, the waterrepellent membrane, and the separator in a state where an outer portionof the water repellent membrane not facing the positive electrode and anouter portion of the separator facing neither the positive electrode northe negative electrode are interposed between a periphery of the firstouter case member and a periphery of the second outer case member.

Effects of the Invention

With this application, it is possible to provide a sheet-type cellexcellent in productivity and a method for manufacturing the same.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view schematically illustrating an example of asheet-type cell of an embodiment.

FIG. 2 is a cross-sectional view taken along the line I-I in FIG. 1.

FIG. 3 is a cross-sectional view taken along the line II-II in FIG. 1.

FIG. 4 is a plan view schematically illustrating another aspect of thesheet-type cell of the embodiment.

FIG. 5 is a cross-sectional view taken along the line III-III in FIG. 4.

FIG. 6 is a cross-sectional view taken along the line IV-IV in FIG. 4.

DESCRIPTION OF THE INVENTION

(Sheet-Type Cell)

The sheet-type cell of this application can be used as various primarycells and secondary cells, and can suitably be used as various cells(such as alkaline cells (alkaline primary cells and alkaline secondarycells), manganese cells, and air cells) including an aqueous electrolytesolution, i.e., an electrolyte solution composed of an aqueous solutioncontaining water as a solvent.

An embodiment of the sheet-type cell of this application will bedescribed. A sheet-type cell of this embodiment includes an outer caseand a power generation element contained in the outer case. The powergeneration element includes a positive electrode, a negative electrode,a separator, and an electrolyte solution. The separator is constitutedby a porous resin sheet. The outer case includes a first outer casemember and a second outer case member. Each outer case member includes athermally fusible resin layer. The first outer case member and thesecond outer case member are disposed on respective opposite sides ofthe power generation element. A periphery of the first outer case memberand a periphery of the second outer case member are sealed by thermallywelding, with a periphery of the separator interposed between theperipheries of the first and second outer case members.

Hereinafter, the sheet-type cell f this embodiment will be describedwith reference to the drawings.

FIGS. 1, 2, and 3 schematically illustrate an example of the sheet-typecell of this embodiment used as an air cell. FIG. 1 is a plan view of asheet-type cell 1. FIG. 2 is a cross-sectional view taken along the lineI-I in FIG. 1. FIG. 3 is a cross-sectional view taken along the lineII-II in FIG. 1.

As illustrated in FIGS. 1.2, and 3, in the sheet-type cell (air cell) 1,a positive electrode 10, a separator 30, a negative electrode 20, and anelectrolyte solution (not illustrated) that constitute a powergeneration element are contained in an outer case (sheet-type outercase) 50. The outer case 50 includes a first outer case member 51 (e.g.,proximate to the positive electrode) and a second outer case member 52(e.g., proximate to the negative electrode), and peripheries of theseare united by thermally welding together.

In this embodiment, the outer case members 51, 52 are formed as separatemembers and disposed on respective opposite sides of the powergeneration element. However, an outer case member may be formed as onecontinuous sheet and be folded to hold the power generation element suchthat the outer case member is disposed on the opposite sides of thepower generation element.

In FIG. 1, the dotted line represents the size of the positive electrode10 (corresponding to the size of a wide main body portion other than aterminal 11 of the positive electrode, i.e., the size of a catalystlayer of the positive electrode described later) contained in the outercase 50.

Moreover, in the sheet-type cell 1, a negative electrode is disposed inthe middle with positive electrodes disposed on opposite sides thereof,or a positive electrode is disposed in the middle with negativeelectrodes disposed on opposite sides thereof.

In FIG. 1, the terminal 11 of the positive electrode 10 and a terminal21 of the negative electrode 20 protrude from the upper side of theouter case 50. The terminals 11, 21 are used to electrically connect thesheet-type cell 1 to the applicable equipment.

The outer case 50 has a plurality of air holes 53 in the side where thepositive electrode 10 is provided so as to take air into the positiveelectrode. A water repellent membrane 40 is provided on the surface ofthe positive electrode 10 that faces the outer case 50 to preventleakage of the electrolyte solution through the air holes 53.

As illustrated in FIGS. 2 and 3, the positive electrode 10, the negativeelectrode 20, the separator 30, the water repellent membrane 40, and theouter case 50 have a single layer structure (FIGS. 5 and 6 describedlater are similar to these figures). However, these components may havea multilayer structure in a sheet-type cell, as described later.

As illustrated in FIGS. 2 and 3, in the sheet-type ell 1, an outerportion (periphery) of the separator 30 facing neither the positiveelectrode 10 nor the negative electrode 20 is interposed between theouter case member 51 proximate to the positive electrode and the outercase member 52 proximate to the negative electrode. In this state, theouter case members 51, 52, and the separator 30 are sealed by thermallywelding together.

As above, in the sheet-type cell of this embodiment, the outer casemembers and the separator are thermally welded together to seal the cellin a state where the outer portion (periphery) of the separator facingneither the positive electrode nor the negative electrode is interposedbetween the outer case member proximate to the positive electrode andthe outer case member proximate to the negative electrode. Thus, theseparator has a sufficiently larger area than the positive electrode andthe negative electrode, thereby permitting some positional deviation ofthe separator. Therefore, the cell productivity can be improved.

The size of the separator (size in a plan view) may be any size thatenables the outer portion thereof to be interposed between the outercase member proximate to the positive electrode and the outer casemember proximate to the negative electrode and enables the outer portionand the outer case members to be thermally welded together. The size ofthe separator may be smaller than those of the outer case memberproximate to the positive electrode and the outer case member proximateto the negative electrode. However, more preferably, the size of theseparator is defined such that ends of the outer case members arealigned with those of the separator as illustrated in FIGS. 2 and 3. Inthis case, when the outer case members are cut, the separator stackedtogether with the outer case members can be cut simultaneously.Therefore, the sheet-type cell is suitable for production by aroll-to-roll method, and the productivity of the sheet-type call can befurther improved.

When the outer case and the separator are rectangular as illustrated inFIG. 1, preferably, an end of one side of the outer case is aligned withthat of the separator, and more preferably, ends of two opposite sidesof the outer case are aligned with those of the separator. Moreover,most preferably, ends of all sides of the outer case are aligned withthose of the separator regardless of their shapes, that is, theseparator and the outer case have the same size in a plan view in termsof production efficiency. FIGS. 2 and 3 illustrate the case where theseparator 30 and the outer case 50 have the same size in a plan view.

Usually, in an air cell, a water repellent membrane is disposed betweena positive electrode and an outer case member proximate to the positiveelectrode. In the sheet-type cell of this embodiment, as illustrated inFIGS. 2 and 3, a size of a water repellent membrane can be adjusted tobe contained in a space within the outer case. The water repellentmembrane can be attached or thermally welded to the entire region whereair holes are provided so as to cover the air holes provided in theouter case member proximate to the positive electrode.

However, when the sheet-type cell of this embodiment is used as an aircell, an outer portion (periphery) of the water repellent membrane notfacing the positive electrode is preferably thermally welded togetherwith the separator in a state where the outer portion and the separatorare interposed between the outer case member proximate to the positiveelectrode and the outer case member proximate to the negative electrodein terms of further improving the productivity of the sheet-type cell.In other words, it is preferable to seal a portion where an outerportion (periphery) of the separator facing neither the positiveelectrode nor the negative electrode is laid on an outer portion(periphery) of the water repellent membrane not facing the positiveelectrode, by thermally welding so as to unite the outer portions andthe peripheries of the outer case members in the portion as a whole.

FIGS. 4, 5, and 6 schematically illustrate another aspect of thesheet-type cell that is different from the previously-describedsheet-type cell of this embodiment used as an air cell. FIG. 4 is a planview of a sheet-type cell 100. FIG. 5 is a cross-sectional view takenalong the line III-III in FIG. 4. FIG. 6 is a cross-sectional view takenalong the line IV-IV in FIG. 4.

As illustrated in FIGS. 4, 5, and 6, in the sheet-type cell (air cell)100, a positive electrode 110, a separator 130, a negative electrode120, and an electrolyte solution (not illustrated) that constitute apower generation element are contained in an outer case (sheet-typeouter case) 150 in the same manner as in the sheet-type cell 1illustrated in FIGS. 1,2, and 3. The outer case 150 includes a firstouter case member 151 (e.g., proximate to the positive electrode) and asecond outer case member 152 (e.g., proximate to the negativeelectrode), and peripheries of these are united by thermally weldingtogether. Also, in this case, an outer case member may be formed as onecontinuous sheet and be folded such that the outer case member isdisposed on opposite sides of the power generation element. In FIG. 4,the dotted line is similar to the dotted line in FIG. 1.

In FIG. 4, a terminal 111 of the positive electrode 110 and a terminal121 of the negative electrode 120 for electrically connecting thesheet-type cell 100 to the applicable equipment protrude from the upperside of the outer case 150. The outer case 150 has a plurality of airholes 153 in the side where the positive electrode 110 is provided so asto take air into the positive electrode. A water repellent membrane 140is provided on the surface of the positive electrode 110 that faces theouter case 150 to prevent leakage of the electrolyte solution throughthe air holes 153 and prevent moisture from entering from outside.

Also, in FIGS. 5 and 6, the positive electrode 110, the negativeelectrode 120, the separator 130, the water repellent membrane 140, andthe outer case 150 have a single layer structure in the same manner asin FIGS. 2 and 3.

In the sheet-type cell 100 illustrated in FIGS. 5 and 6, an outerportion (periphery) of the water repellent membrane 140 not facing thepositive electrode 110 is thermally welded together with an outerportion (periphery) of the separator 130 facing neither the positiveelectrode 110 nor the negative electrode 120 to seal the cell in a statewhere the outer portions are interposed between the outer case member151 proximate to the positive electrode and the outer case member 152proximate to the negative electrode. Thus, the separator and the waterrepellent membrane have a sufficiently larger area than the positiveelectrode and the negative electrode, thereby permitting some positionaldeviation of the separator and that of water repellent membrane.Therefore, the cell productivity can be further improved.

In the case of the sheet-type cell (air cell) illustrated in FIGS. 5 and6, the size of the water repellent membrane (size in a plan view) may beany size that enables the outer portion thereof to be interposed betweenthe outer case member proximate to the positive electrode and the outercase member proximate to the negative electrode and enables the outerportion and the outer case members to be thermally welded together. Thesize of the water repellent membrane may be smaller than those of theouter case member proximate to the positive electrode and the outer casemember proximate to the negative electrode. However, more preferably,the size of the water repellent membrane is defined such that ends ofthe outer case are aligned with those of the water repellent membrane asillustrated in FIGS. 5 and 6. In this case, when the outer case membersare cut, the water repellent membrane stacked together with the outercase members can be cut simultaneously. Therefore, the productivity ofthe sheet-type cell can be further improved.

When the outer case and the water repellent membrane are rectangular asillustrated in FIG. 4, preferably, an end of one side of the outer caseis aligned with that of the water repellent membrane, and morepreferably, ends of two opposite sides of the outer case are alignedwith those of the water repellent membrane. When the outer case, thewater repellent membrane and the separator are rectangular, preferably,an end of one side of the outer case is aligned with that of the waterrepellent membrane and that of the separator, and more preferably, endsof two opposite sides of the outer case are aligned with those of thewater repellent membrane and the separator. Particularly preferably,ends of all sides of the water repellent membrane and the outer case arealigned with each other regardless of their shapes, that is, the waterrepellent membrane and the outer case have the same size in a plan view.Most preferably, ends of all sides of the water repellent membrane, theseparator, and the outer case are aligned with each other regardless oftheir shapes, that is, the water repellent membrane, the separator, andthe outer case have the same size in a plan view. FIGS. 5 and 6illustrate the case where the water repellent membrane 140 has the samesize as the separator 130 and the outer case 150 in a plan view.

Next, the components and their related matters of the sheet-type cell ofthis embodiment will be described.

<Separator>

As the separator of the sheet-type cell of this embodiment, a porousresin sheet is used. Examples of the porous resin sheet include a porousresin film (e.g., a microporous film for a separator or a membrane for afilter) and a resin nonwoven fabric. The separator may be a stack of theporous film and the nonwoven fabric.

The porous resin sheet is preferably made of a resin that fuses at atemperature of 200° C. or less (i.e., a resin having a meltingtemperature of 200° C. or less measured in accordance with the JapaneseIndustrial Standards (JIS) K 7121) in terms of enhancing thermallywelding properties.

Specific examples of the resin of the porous resin sheet includepolyolefins such as polyethylene (PE) and polypropylene (PP), and anethylene-propylene copolymer.

The air permeability of the separator is preferably 3000 sec/100 ml orless in terms of achieving good ion permeability, and preferably 10sec/100 ml or more in terms of ensuring good strength.

In this specification, the air permeability of the separator and the airpermeability of the water repellent membrane (described later) can bedetermined by the Gurley method specified in JIS P 8117.

The porosity of the separator is preferably 30% to 80%. Moreover, thethickness of the separator is preferably 10 to 100 μm.

<Water Repellent Membrane>

When the sheet-type cell of this embodiment is an air cell, the waterrepellent membrane has not only water repellency, but also airpermeability. Specific examples of the water repellent membrane includea membrane (porous film) made of a resin such as fluororesin (e.g.,polytetrafluoroethylene (PTFE)) or polyolefins (e.g., polypropylene andpolyethylene). Moreover, the water repellent membrane can be of amultilayer structure in which a porous polyolefin layer is provided on aporous resin base (e.g., a nonwoven fabric made of polyester such aspolyethylene terephthalate (PET) or a polyolefin).

As illustrated in FIGS. 5 and 6, in the sheet-type cell in which thewater repellent membrane is thermally welded together with theseparator, the water repellent membrane preferably includes a porouslayer made of a resin that fuses at a temperature of 200° C. or less(i.e., a resin having a melting temperature of 200° C. or less measuredin accordance with JIS K 7121) in terms of enhancing thermally weldingproperties. Examples of such a water repellent membrane include amembrane (porous film) formed of only a parous layer made of a resinthat fuses at a temperature of 200° C. or less and a membrane having amultilayer structure in which the porous layer made of a resin thatfuses at a temperature of 200° C. or less is provided on a porous resinbase. As the resin that fuses at a temperature of 200° C. or less, apolyolefin such as polypropylene or polyethylene can be used. As theresin of the porous resin base, polyester such as polyethyleneterephthalate (PET) can be used, for example.

The air permeability of the water repellent membrane is preferably 60000sec/100 ml or less in terms of achieving good permeability for air(oxygen). Moreover, the air permeability thereof is preferably 20sec/100 ml or more, more preferably 1000 sec/100 ml or more, andparticularly preferably 3000 sec/100 ml or more in terms of preventingleakage of the electrolyte solution and ensuring good strength.

The thickness of the water repellent membrane is preferably 50 to 250μm.

<Positive Electrode>

When the sheet-type cell is an alkaline cell or a manganese cell, thepositive electrode of the sheet-type cell of this embodiment may have astructure in which a positive electrode mixture layer containing, e.g.,a positive electrode active material, a conductive assistant, and abinder is formed on one side or both sides of a current collector.Examples of the positive electrode active material include silver oxides(such as silver (I)oxide and silver (II) oxide), manganese oxides suchas manganese dioxide, nickel oxyhydroxide, and composite oxides ofsilver and cobalt, nickel, or bismuth.

Examples of the conductive assistant of the positive electrode mixturelayer include the following: carbon materials such as carbon blacks ofacetylene black, Ketjenblack, channel black, furnace black, lamp black,thermal black, etc. and carbon fibers; conductive fibers such asmetallic fibers; carbon fluoride; metal powders of copper, nickel, etc.;and organic conductive materials such as polyphenylene derivatives.

Examples of the binder of the positive electrode mixture layer includethe following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene(PTFE), styrene-butadiene rubber (SBR), carbaoxymethyl cellulose (CMC),and polyvinylpyrrolidone (PVP).

In the composition of the positive electrode mixture layer, the amountof the positive electrode active material is preferably 80 to 98% bymass, the content of the conductive assistant is preferably 1.5 to 10%by mass, and the content of the binder is preferably 0.5 to 10% by mass.The thickness of the positive electrode mixture layer is preferably 30to 300 μm (per one side of the current collector).

The positive electrode having the positive electrode mixture layer canbe produced in the following manner. For example, the positive electrodeactive material, the conductive assistant, and the binder are dispersedin water or an organic solvent such as N-methyl-2-pyrrolidone (NMP) toprepare a positive electrode mixture containing composition, e.g., inthe form of slurry or paste (in this case, the binder may be dissolvedin the solvent). This composition is applied to the current collector,dried, and optionally subjected to pressing such as calendering.

When the sheet-type cell of this embodiment is an air cell, the positiveelectrode (air electrode) has a catalyst layer. For example, thepositive electrode with a laminated structure of the catalyst layer andthe current collector may be used.

The catalyst layer may contain, e.g., a catalyst and a binder.

Examples of the catalyst of the catalyst layer include the following:silver, platinum metals or alloys thereof transition metals;platinum/metal oxides such as Pt/IrO₂; perovskite oxides such asLa_(1-x)Ca_(x)CoO₃; carbides such as WC; nitrides such as Mn₄N;phthalocyanine compound metal complexes; manganese oxides such asmanganese dioxide; and carbon (including, e.g., graphite, carbon black(acetylene black, Ketjenblack, channel black, furnace black, lamp black,thermal black, etc.), charcoal, and activated carbon). These catalystsmay be used alone or in combinations of two or more.

The heavy metal content in the catalyst layer, except for the componentsof the electrolyte, is preferably 1% by mass or less. When the positiveelectrode has the catalyst layer with a low heavy metal content, theenvironmental impact can be reduced even if the cell is disposed ofwithout any special treatment.

In this specification, the heavy metal content in the catalyst layer canbe measured by X-ray fluorescence analysis. For example, the measurementcan be performed using an X-ray fluorescence analyzer “ZSX100e”manufactured by Rigaku Corporation under the following conditions:excitation source, Rh 50 kV; and analysis area, φ 10 mm.

It is recommended that the catalyst of the catalyst layer should containno heavy metal, but preferably contain the various types of carbon asdescribed above.

In terms of further improving the reactivity of the positive electrode,the specific surface area of the carbon that is used as the catalyst ispreferably 200 m²/g or more, more preferably 300 m²/g or more, andfurther preferably 500 m²/g or more. In this specification, the specificsurface area of the carbon is determined by a BET method in accordancewith JIS K 6217. For example, the specific surface area of the carboncan be measured with a specific surface area measuring device (“MacsorbHM model-1201” manufactured by Mountech Co., Ltd) based on a nitrogenadsorption method. The upper limit of the specific surface area of thecarbon is usually about 2000 m²/g.

The content of the catalyst in the catalyst layer is preferably 20 to70% by mass.

Examples of the binder of the catalyst layer include fluorocarbon resinbinders such as PVDF, PTFE, copolymers of vinylidene fluoride, andcopolymers of tetrafluoroethylene (including, e.g., a vinylidenefluoride-hexafluoropropylene copolymer (PVDF-HFP), a vinylidenefluoride-chlorotrifluoroethylene copolymer (PVDF-CTFE), a vinylidenefluoride-tetrafluoroethylene copolymer (PVDF-TFE), and a vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene copolymer(PVDF-HFP-TFE)). Among them, polymers of tetrafluoroethylene (PTFE) orcopolymers of tetrafluoroethylene are preferred, and PTFE is morepreferred. The content of the binder in the catalyst layer is preferably3 to 50% by mass.

The positive electrode of the air cell can be produced by, e.g., mixingthe above catalyst, binder, or the like with water, rolling the mixturebetween rotating rolls, and bringing the rolled material into closecontact with the current collector. There may be another way ofproducing the positive electrode, as follows. First, a composition(slurry, paste, etc.) for forming a catalyst layer is prepared bydispersing, the above catalyst and optionally the binder or the like inwater or an organic solvent. Then, the composition is applied to thesurface of the current collector and dried, which is further subjectedto pressing (e.g., calendering) as needed.

The catalyst layer may be a porous carbon sheet made of fibrous carbonsuch as carbon paper, carbon cloth, or carbon felt. The carbon sheet canalso be used as a current collector of the positive electrode, as willbe described later. The carbon sheet can serve as both the catalystlayer and the current collector.

The current collector of the positive electrode may be, e.g., a mesh,foil, expanded metal, or punched metal made of metals such as titanium,nickel, stainless steel, and copper or may be, e.g., a mesh or sheetmade of carbon. The thickness of the current collector of the positiveelectrode is preferably 10 μm or more and 300 μm or less.

The current collector of the positive electrode can be provided byapplying a carbon paste to an inner surface of the outer case. When theouter case members constituting the outer case include a metal layer,the metal layer can be a current collector. In either case, the positiveelectrode mixture layer or the catalyst layer can be formed on thesurface of the current collector in the same manner as described above,thus producing a positive electrode. The thickness of the currentcollector made of the carbon paste is preferably 30 to 300 μm.

<Negative Electrode>

The negative electrode of the sheet-type cell of this embodiment maycontain a metal material. Examples of the metal material include thefollowing: a zinc-based material (which collectively refers to both azinc material and a zinc alloy material); a magnesium-based material(which collectively refers to both a magnesium material and a magnesiumalloy material); and an aluminum-based material (which collectivelyrefers to both an aluminum material and an aluminum alloy material). Inthis negative electrode, metals such as zinc, magnesium, and aluminumact as an active material.

Specifically, the negative electrode containing the metal material maybe a negative electrode containing metal particles such as zinc-basedparticles (which collectively refer to both zinc particles and zincalloy particles), magnesium-based particles (which collectively refer toboth magnesium particles and magnesium alloy particles), andaluminum-based particles (which collectively refer to both aluminumparticles and aluminum alloy particles).

Examples of the alloy constituents of the zinc alloy particles includeindium (the content is, e.g., 0.005 to 0.05% by mass), bismuth (thecontent is, e.g., 0.005 to 0.2% by mass), and aluminum (the content is,e.g., 0.001 to 0.15% by mass).

Examples of the alloy constituents of the magnesium alloy particlesinclude calcium (the content is, e.g., 1 to 3% by mass), manganese (thecontent is, e.g., 0.1 to 0.5% by mass), zinc (the content is, e.g., 0.4to 1% by mass), and aluminum (the content is, e.g., 8 to 10% by mass).

Examples of the alloy constituents of the aluminum alloy particlesinclude zinc (the content is, e.g., 0.5 to 10% by mass), tin (thecontent is, e.g., 0.04 to 1.0% by mass), gallium (the content is, e.g.,0.003 to 1.0% by mass), silicon (the content is, e.g., 0.05% by mass orless), iron (the content is, e.g., 0.1% by mass or less), magnesium (thecontent is, e.g., 0.1 to 2.0% by mass), and manganese (the content is,e.g., 0.01 to 0.5% by mass).

The negative electrode may contain only one type of metal particles ortwo or more types of metal particles.

In view of a reduction in the environmental impact of the cell fordisposal, it is preferable that the metal material used for the negativeelectrode contains the smallest possible amount of mercury, cadmium,lead, and chromium. Specifically, it is more preferable that the mercurycontent is 0.1% by mass or less, the cadmium content is 0.01% by mass orless, the lead content is 0.1% by mass or less, and the chromium contentis 0.1% by mass or less.

The particle size of the zinc-based particles may be defined as follows.For example, the proportion of the particles with a particle diameter of75 μm or less is preferably 50% by mass or less, and more preferably 30%by mass or less of all particles. Moreover, the proportion of theparticles with a particle diameter of 100 to 200 μm may be 50% by massor more, and more preferably 90% by mass or more of all particles.

Moreover, the particle size of the magnesium-based particles and thealuminum-based particles may be defined as follows. For example, theproportion of the particles with a particle diameter of 30 μm or less ispreferably 50% by mass or less, and more preferably 30% by mass or lessof all articles. Moreover, the proportion of the particles with aparticle diameter of 50 to 200 μm may be 50% by mass or more, and morepreferably 90% by mass or more of all particles.

In the present specification, the particle size of the metal particlesmeans a particle diameter (D₅₀) at a cumulative frequency of 50% in thevolume-based distribution, which is measured with a laser scatteringparticle size distribution analyzer (e.g., “LA-920” manufactured byHORIBA, Ltd.) by dispersing the particles in a medium that does notdissolve those particles.

When the negative electrode contains the metal particles, for example, athickening agent (e.g., any of later-described thickening agents thatcan be used to produce a gel electrolyte) and a binder may be added asneeded. This may be mixed with an electrolyte solution to form anegative electrode agent (such as a gel-like negative electrode). Theamount of the thickening agent in the negative electrode is preferably,e.g., 0.5 to 1.5% by mass. The amount of the binder in the negativeelectrode is preferably 0.5 to 3% by mass.

The electrolyte solution used for the negative electrode containing themetal particles may be the same as that described later.

The content of the metal particles in the negative electrode ispreferably, e.g., 60% by mass or more, and more preferably 65% by massor more. The content of the metal particles in the negative electrode isalso preferably 95% by mass or less, and more preferably 90% by mass orless.

The negative electrode containing the metal particles preferablycontains an indium compound. The presence of the indium compound in thenegative electrode can more effectively prevent the generation ofhydrogen gas due to a corrosion reaction between the metal particles andthe electrolyte.

Examples of the indium compound include indium oxide and indiumhydroxide.

The amount of the indium compound in the negative electrode ispreferably 0.003 to 1 with respect to 100 of the metal particles at amass ratio.

The negative electrode may also be a metal sheet such as a zinc-basedsheet (e.g., zinc foil or zinc alloy foil) or a magnesium-based sheet(e.g., magnesium fil or magnesium alloy foil). Such a negative electrodepreferably has a thickness of 10 to 500 μm.

The composition of the zinc-based sheet can be the same as that of thezinc-based particles. The composition of the magnesium-based sheet canbe the same as that of the magnesium-based particles. However, thezinc-based sheet is preferably made of a zinc alloy containing at leastbismuth in order to suppress the reaction with the electrolyte solution.The content of bismuth in the zinc alloy is preferably 0.005 to 0.1% bymass.

The negative electrode containing the metal material may include acurrent collector as needed. The current collector of the negativeelectrode may be, e.g., a mesh, fail, expanded metal, or punched metalmade of metals such as nickel, copper, and stainless steel or may be,e.g., a sheet or mesh made of carbon. The thickness of the currentcollector of the negative electrode is preferably 10 μm or more 300 μmor less.

The current collector of the negative electrode can be provided byapplying a carbon paste to an inner surface of the outer case in thesame as that of the positive electrode. When the outer case membersconstituting the outer case include a metal layer, the metal layer canbe a current collector like that of the positive electrode. Thethickness of the current collector made of the carbon paste ispreferably 50 to 200 μm.

<Electrolyte Solution>

As the electrolyte solution of the sheet-type cell of this embodiment,an aqueous solution containing an electrolyte salt is used. When thesheet-type cell is a manganese cell or an air cell, the pH of theaqueous solution used as the electrolyte solution is preferably 3 ormore, more preferably 4 or more, and particularly preferably 5 or more.The pH of the aqueous solution is preferably less than 12, morepreferably 10 or less, and further preferably less than 7. Compared to,e.g., a strong alkaline aqueous solution with a high pH (a pH of about14) commonly used in air cells, the aqueous solution having a pH withinthe above range is less likely to cause a problem even if theelectrolyte adheres to a human body due to the fracture of the cell whendiscarded or in use. The aqueous solution can ensure high safety andreduce the environmental impact after disposal.

Meanwhile, when the sheet-type cell is an alkaline cell, the pH of theelectrolyte solution can be as high as 12 or more, and even. e.g., 14 ormore.

When the sheet-type cell is an air cell or a manganese cell, examples ofthe electrolyte salt dissolved in the aqueous solution used as theelectrolyte solution include the following: chlorides such as sodiumchloride, potassium chloride, magnesium chloride, calcium chloride,ammonium chloride, and zinc chloride; hydroxides of alkali metals oralkaline-earth metals (e.g., sodium hydroxide, potassium hydroxide, andmagnesium hydroxide), acetates of these (e.g., sodium acetate, potassiumacetate, and magnesium acetate), nitrates of these (e.g., sodiumnitrate, potassium nitrate, and magnesium nitrate), sulfates of these(e.g., sodium sulfate, potassium sulfate, and magnesium sulfate),phosphates of these (e.g., sodium phosphate, potassium phosphate, andmagnesium phosphate), borates of these (e.g., sodium borate, potassiumborate, and magnesium borate), citrates of these (e.g., sodium citrate,potassium citrate, and magnesium citrate), and glutamates of these(e.g., sodium glutamate, potassium glutamate, and magnesium glutamate);hydrogencarbonates of alkali metals (e.g., sodium hydrogencarbonate andpotassium hydrogencarbonate); percarbonates of alkali metals (e.g.,sodium percarbonate and potassium percarbonate); compounds containinghalogens such as fluorides; and polycarboxylic acids. The aqueoussolution may contain either one or two or more of these electrolytesalts.

When the sheet-type cell is an air cell, the aqueous solution that canbe used as the electrolyte solution preferably contains a water-solublehigh-boiling solvent with a boiling point of 150° C. or more along withwater. As the air cell is discharged, the voltage decreases with adecrease in the capacity. In the late stage of discharge, since thecapacity of the air cell becomes smaller, the voltage not only decreasesbut also tends to vary greatly. However, the presence of thewater-soluble high-boiling solvent in the aqueous solution can suppresssuch a voltage variation in the late stage of discharge. Thus, thesheet-type air cell can have better discharge characteristics. The upperlimit of the boiling point of the water-soluble high-boiling solvent isusually 320° C.

It is desirable that the water-soluble high-boiling solvent has a highsurface tension and a high relative dielectric constant. Specificexamples of the water-soluble high-boiling solvent include thefollowing: polyhydric alcohols such as ethylene glycol (boiling point:197° C., surface tension: 48 mN/m, relative dielectric constant: 39),propylene glycol (boiling point: 188° C., surface tension: 36 mN/m,relative dielectric constant: 32), and glyceol (boiling point: 290° C.,surface tension: 63 mN/m, relative dielectric constant: 43); andpolyalkylene glycol (having a molecular weight of preferably 600 orless) such as polyethylene glycol (e.g., boiling point: 230° C., surfacetension: 43 mN/m, relative dielectric constant: 35). The electrolytesolution may contain either only one or two or more of thesewater-soluble high-boiling solvents, and more preferably may containglycerol.

To satisfactorily ensure the effect of the water-soluble high-boilingsolvent when it is used, the content of the water-soluble high-boilingsolvent in the aqueous solution is preferably 1% by mass or more, andmore preferably 3% by mass or more of the total solvent. However, if theamount of the water-soluble high-boiling solvent in the aqueous solutionis too large, the ionic conduction of the aqueous solution becomes toosmall, so that the cell characteristics may be reduced. Thus, thecontent of the water-soluble high-boiling solvent in the aqueoussolution is preferably 30% by mass or less, and more preferably 20% bymass or less of the total solvent.

The concentration of the electrolyte salt in the aqueous solution may beset so that the conductivity of the aqueous solution can be adjusted,e.g., to about 80 to 700 mS/cm. The concentration of the electrolytesalt is usually 5 to 50% by mass.

When the sheet-type cell is an alkaline cell, the electrolyte solutionmay be an alkaline electrolyte solution. Specifically, the alkalineelectrolyte solution may be, e.g., an alkaline aqueous solution composedof an aqueous solution of alkali metal hydroxide such as potassiumhydroxide, sodium hydroxide, or lithium hydroxide. The alkalineelectrolyte solution may also be obtained by adding zinc oxide to thealkaline aqueous solution. The concentration of the alkali metalhydroxide in the alkaline electrolyte solution is preferably 28 to 38%by mass in the case of e.g., potassium hydroxide. When the alkalineelectrolyte solution contains zinc oxide, the concentration of the zincoxide is preferably 1.0 to 4.0% by mass.

It is preferable that an indium compound is dissolved in the solvent(water or a mixed solvent of water and the water-soluble high-boilingsolvent) of the aqueous solution used as the electrolyte solution. Whenthe indium compound is dissolved in the aqueous solution, the generationof hydrogen gas inside the cell can be adequately suppressed.

Examples of the indium compound dissolved in the aqueous solutioninclude indium hydroxide, indium oxide, indium sulfate, indium sulfide,indium nitrate, indium bromide, and indium chloride.

The concentration of the indium compound in the aqueous solution ispreferably 0.005% by mass or more, mom preferably 0.01% by mass or more,and particularly preferably 0.05% by mass or more. The concentration ofthe indium compound in the aqueous solution is also preferably 1% bymass or less, more preferably 0.5% by mass or less, and particularlypreferably 0.1% by mass or less.

In addition to the above described components, the aqueous solution mayoptionally contain various known additives. For example, zinc oxide maybe added to the aqueous solution to prevent corrosion (oxidation) of themetal material used for the negative electrode.

The aqueous solution used as the electrolyte solution may be gelled, anda gel electrolyte solution (gel electrolyte) is also preferably used asthe electrolyte solution of the sheet-type cell. The gel electrolytesolution may be prepared by mixing the aqueous solution containing theelectrolyte salt and a thickening agent (such as sodium polyacrylate,carboxymethyl cellulose, or polyoxyethylene). The use of the gelelectrolyte solution can also suppress the voltage variation in the latestage of discharge and can further improve the discharge characteristicsof the sheet-type cell. When the sheet-type cell is an air cell, thevaporization of water from the gel electrolyte solution is reduced.Therefore, it is possible to suppress a reduction in the dischargecharacteristics due to the composition change of the electrolytesolution, and to further improve the storage characteristics of thesheet-type air cell.

<Outer Case>

As long as the outer case members constituting the outer case of thesheet-type cell of this embodiment include a thermally fusible resinlayer in their thermally welded portion, the specific configurations ofthe outer case members are not limited. For example, a laminated filmobtained by stacking a thermally fusible resin layer (which ishereinafter also referred to as a thermal fusion resin layer) on a resinlayer that is to be a base (which is hereinafter also referred to as abase resin layer) can be used as each of the outer case members.

The outer case is sealed by thermally welding the ends of the firstouter case member (e.g., proximate to the positive electrode) and thoseof the second outer case member (e.g., proximate to the negativeelectrode) together. When each outer case member is the laminated film,the thermally welded portion is on the side of the thermal fusion resinlayer. Thus, the thermal fusion resin layer of the outer case member isdisposed on each of the inner surfaces of the outer case.

The thermal fusion resin layer can be made of a resin that fuses at atemperature of 200° C. or less. When the resin that fuses at atemperature of 200° C. or less has a melting point, the resin is a resinhaving a melting temperature of 200° C. or less measured in accordancewith JIS K 7121. When the resin that fuses at a temperature of 200° C.or less does not have a melting point, the resin is a resin having aglass transition temperature of 200° C. or less measured in accordancewith JIS K 7121. Specific examples of the resin that fuses at atemperature of 200° C. or less include polyolefins such as polyethyleneand polypropylene, and modified polyolefins (such as modified polyolefinionomers). The thickness of the thermal fusion resin layer is preferably20 to 100 μm.

The base resin layer is made of a resin having a higher melting point orglass transition temperature than the thermal fusion resin layer.Specific examples of the base resin layer include a nylon film (e.g., anylon 66 film) and a polyester film (e.g., a polyethylene terephthalate(PT film). The thickness of the base resin layer is preferably 20 to 100μm.

Moreover, when each outer case member is formed of the laminated film, ametal layer may further be formed thereon. The metal layer may be madeof e.g., a vapor deposited film of aluminum (including an aluminumalloy), an aluminum film (including an aluminum foil and aluminum alloyfoil) or a stainless steel film (including a stainless steel foil). Thethickness of the metal layer is preferably 10 to 150 μm.

When each outer case member is formed of the laminated film, anelectrically insulating oxide layer may further be disposed on a surfaceof the base resin layer that is opposite to the thermal fusion resinlayer in order to prevent the permeation of moisture through the outercase members.

Examples of an oxide of the electrically insulating oxide layer includeinorganic oxides such as aluminum oxide and silicon oxide. A layercomposed of silicon oxide tends to be superior to that composed ofaluminum oxide in the function of suppressing the permeation of moisturein the electrolyte solution of the cell. For this reason, theelectrically insulating oxide layer is more preferably a layer composedof silicon oxide.

The electrically insulating oxide layer can be formed on an outersurface of the base resin layer by, e.g., an evaporation method. Thethickness of the electrically insulating oxide layer is preferably 10 to300 nm.

When the outer case members have the electrically insulating oxidelayer, a protective layer for protecting the oxide layer may be formedon a surface of the oxide layer that is opposite to the base resinlayer.

As the outer case member having the electrically insulating oxide layer,it is possible to use laminated films that are commercially availableunder the name of, e.g., barrier films for use in medical applications,electronic devices, food, etc. The commercially available barrier filmsare laminated films formed of a three layered structure of the oxidelayer, the base resin layer, and the thermal fusion resin layer.

Examples of the commercially available barrier films can include, e.g.,“GL FILM” and “PRIME BARRIER” (both are trade names) manufactured byToppan Printing CO., LTD., “MAXBARRIER” and “TL” (both are trade names)manufactured by Mitsui Chemicals Tohcello, Inc., “TECHBARRIER” (tradename) manufactured by Mitsubishi Chemical Corporation, “IB-Film” (tradename) manufactured by Dai Nippon Printing Co., Ltd., and “ECOSYAL”(trade name) manufactured by TOYOBO CO., LTD.

The shape of the outer case may be, e.g., a polygon (such as triangle,quadrangle, pentagon, hexagon, heptagon, or octagon), a circle, or anellipse in a plan view. When the outer case has a polygonal shape in aplan view, the terminal of the positive electrode and the terminal ofthe negative electrode may be drawn from the same side or differentsides of the outer case to the outside.

<Air Diffusion Membrane>

When the sheet-type cell of this embodiment is an air cell, an airdiffusion membrane may be disposed between the outer case and the waterrepellent membrane. The air diffusion membrane serves to supply the airthat has been taken into the outer case to the positive electrode. Theair diffusion membrane may be, e.g., a nonwoven fabric made of a resinsuch as cellulose, polyvinyl alcohol, polypropylene, or nylon. Thethickness of the air diffusion membrane is preferably 100 to 250 μm.

<Others>

The thickness of the sheet-type cell (i.e., the length indicated by theletter a in FIGS. 3 and 6) is not particularly limited and may beappropriately changed depending on the use of the cell. One of theadvantages of the cell having the sheet-type outer case is that thethickness can be reduced. In view of this, the thickness of thesheet-type cell is preferably, e.g., 1 mm or less.

The lower limit of the thickness of the sheet-type cell is notparticularly limited, and may usually be 0.2 mm or more to maintain apredetermined amount of capacity.

(Method for Manufacturing Sheet-Type Cell)

Next, an embodiment of a method for manufacturing a sheet-type cell ofthis application will be described.

A first method for manufacturing a sheet-type cell of this embodiment isa method for manufacturing the above-described sheet-type cell of thisapplication. The first manufacturing method includes disposing the firstouter case member and the second outer case member on the respectiveopposite sides of the power generation element, and thermally welding toseal the first and second outer case members disposed on the respectiveopposite sides of the power generation element and the separator in astate where the outer portion of the separator facing neither thepositive electrode nor the negative electrode is interposed between theperiphery of the first outer case member and the periphery of the secondouter case member.

With the first manufacturing method, it is possible to manufacture,e.g., the sheet-type cell illustrated in FIGS. 1-3.

A second method for manufacturing a sheet-type cell of this embodimentis a method for manufacturing the above-described sheet-type cell(sheet-type air cell) of this application. The second manufacturingmethod includes disposing the first outer case member and the secondouter case member on the respective opposite sides of the powergeneration element provided with the water repellent membrane on theouter surface of the positive electrode in the power generation element,and thermally welding to seal the first and second outer case membersdisposed on the respective opposite sides of the power generationelement, the water repellent membrane, and the separator in a statewhere the outer portion of the water repellent membrane not facing thepositive electrode and the outer portion of the separator facing neitherthe positive electrode nor the negative electrode are interposed betweenthe periphery of the first outer case member and the periphery of thesecond outer case member.

With the second manufacturing method, it is possible to manufacture,e.g., the sheet-type cell (sheet-type air cell) illustrated in FIGS.4-6.

EXAMPLES

First, experimental results in which sealing properties of outer casesof sheet-type cells were evaluated will be described as referenceexperiments.

Experimental Example 1

A barrier film (manufactured by Toppan Printing CO., LTD), apolypropylene nonwoven fabric (thickness: 100 μm, melting point: 200° C.or less), and a polyethylene porous film (thickness: 80 μm, meltingpoint: 150° C. or less, air permeability: 15000 sec/100 ml) wererespectively cut into a size of 24 mm×24 mm to prepare two outer casemembers, a separator, and a water repellent membrane. The barrier filmwas a laminated film formed of a 15 μm nylon layer (base resin layer), a40 μm polyethylene layer (thermal fusion resin layer having a meltingpoint of 150° C. or less), and a 12 μm polyethylene terephthalate layerin which a deposited silica layer (oxide layer) was formed on the sideof the base resin layer. The two outer case members had theabove-described size. The polyethylene layer of each of the outer casemembers was disposed inside. A stack was formed by laying one of theouter case members, the separator, the water repellent membrane, and theother outer case member in this order. Then, a portion 5 mm in widthfrom ends of three sides of the outer case members, the separator, thewater repellent membrane along their peripheries were thermally weldedtogether.

Next, a solution was prepared as an electrolyte solution by dissolving20% by mass of ammonium chloride in a mixed solvent of water andglycerol (glycerol: 10% by mass). After 0.1 ml of the electrolytesolution was injected through an opening (remaining one side) of thestack, the opening was thermally welded 5 mm in width from an end of theone side to seal an outer case. Furthermore, a portion 2 mm in widthfrom the outer edge of the outer case in the periphery of the outer casethat was sealed by thermally welding was cut to produce an outer casefor evaluation having a size of 20 mm×20 mm and the periphery that wassealed by thermally welding 3 mm in width.

In Experimental example 1, an outer case was produced by thermallywelding at a temperature of 170° C. and an outer case was produced bythermally welding at a temperature of 200° C. to evaluate the differencein sealing properties due to thermally welding temperatures (theevaluation was similarly performed in each experimental exampledescribed later).

Experimental Example 2

An outer case for evaluation was produced in the same manner as inExperimental example 1 except that the water repellent membrane waschanged to a PTFE porous film having a thickness of 80 μm.

Experimental Example 3

An outer case for evaluation was produced in the same manner as inExperimental example 1 except that the separator was changed to acommercially available polyethylene microporous film (melting point:150° C. or less) and a water repellent membrane was not used.

Experimental Example 4

An outer case for evaluation was produced in the same manner as inExperimental example 2 except that the separator was changed to acellophane film.

Experimental Example 5

An outer case for evaluation was produced in the same manner as inExperimental example 1 except that a separator and a water repellentmembrane were not used and two outer case members were thermally weldedto each other directly.

Sealing properties of the outer cases for evaluation of each ofExperimental examples 1 to 5 were evaluated as below. Each outer casefor evaluation was stored in a thermostat at 60° C., and then, areduction in weight one day after the start of the storage of the outercase was measured to obtain a vaporization amount of the electrolytesolution. The proportion of the vaporization amount of the electrolytesolution to a weight of the electrolyte solution in the outer case forevaluation before storing was obtained as a “vaporization proportion ofelectrolyte solution” in order to evaluate the sealing properties of theouter case for evaluation. A “vaporization proportion of electrolytesolution” of the outer case for evaluation of each of Experimentalexamples 1, 3, and 5 was obtained by measuring not only the reductiondescribed above but also a reduction in weight seven days after thestart of the storage.

Table 1 indicates the evaluation results. The sign×indicates that anouter case for evaluation was not able to be thermally welded andleakage of the electrolyte solution was confirmed.

TABLE 1 Thermally welding Vaporization proportion of electrolytetemperature solution (%) (° C.) One day after Seven days afterExperimental 170 2 8 example 1 200 0 4 Experimental 170 55  — example 2200 45  — Experimental 170 1 7 example 3 200 1 4 Experimental 170 x xexample 4 200 x x Experimental 170 1 2 example 5 200 0 2

In the outer cases for evaluation of Experimental example 4 in which thecellophane film was used as the separator and the PTFE porous film wasused as the water repellent membrane, the peripheries of the two outercase members were not able to be thermally welded at all. On the otherhand, in the outer cases for evaluation of Experimental example 2, thepolypropylene nonwoven fabric having a melting point of 200° C. or lesswas used as the separator instead of a cellophane film and the PTFEporous film was used as the water repellent membrane similarly. Althoughthe PTFE porous film was used as the water repellent membrane, in theouter case for evaluation of Experimental example 2 produced bythermally welding at 200° C., the peripheries of the two outer casemembers were able to be thermally welded together in a state where thewater repellent membrane and the separator were interposed between theouter case members, and the outer case had some degree of sealingproperties.

In the outer cases for evaluation of Experimental example 3, only thepolyethylene microporous film having a melting point of 150° C. or lesswas interposed between the two outer case members. In the outer casesfor evaluation of Experimental example 1, the polyethylene porous film(water repellent membrane) having a melting point of 150° C. or less andthe polypropylene nonwoven fabric (separator) having a melting point of200° C. or less were interposed between the two outer case members. Inthe outer case for evaluation of Experimental example 3 and the outercase for evaluation of Experimental example 1 that were produced bythermally welding at 200° C., the peripheries of the outer case memberswere able to be thermally welded together more satisfactorily, and theouter cases had excellent sealing properties similarly to the outercases for evaluation of Experimental example 5 in which the two outercase members were thermally welded to each other directly.

Next, the sheet-type cell of this application will be described indetail based on examples. However, the sheet-type cell of thisapplication is not limited to the following examples.

Example

<Negative Electrode>

A negative electrode was produced by cutting an electrolytic zine foilhaving a thickness of 50 μm into a main body portion having a size of 15mm×15 mm and a shape having a terminal portion of 5 mm in width×15 mm inlength.

<Positive Electrode>

A composition for forming a catalyst layer was prepared by mixing 100parts by mass of carbon black (“Ketjenblack EC600JD (trade name)”manufactured by Lion Specialty Chemicals Co., Ltd.) with a DBP oilabsorption of 495 cm³/100 g and a specific surface area of 1270 m²/g, 1part by mass of phthalocyanine metal complex, 25 parts by mass of adispersing agent, and 5000 parts by mass of ethanol.

Using porous carbon paper (thickness: 0.25 mm, porosity: 75%, airpermeability (Gurley): 70 sec/100 ml) as a current collector, thecomposition for forming a catalyst layer was applied to the surface ofthe current collector by stripe coating so that the coating amount afterdrying was 10 mg/cm². Then, the composition was dried, resulting in thecurrent collector that had a portion in which the catalyst layer wasformed and a portion in which no catalyst layer was formed. This currentcollector was punched into a shape including the portion with thecatalyst layer that was 15 mm×15 mm in size and the portion without thecatalyst layer having a size of 5 mm in width×15 mm in length. Theportion without the catalyst layer was to be a terminal. Thus, apositive electrode (air electrode) with a total thickness of 0.27 mm wasproduced.

<Separator>

A polypropylene nonwoven fabric with a thickness of 100 μm was madehydrophilic for an alkaline storage cell, was cut into 25 mm×25 mm, andwas used as a separator.

<Water Repellent Membrane>

A polyethylene porous film that was the same as that of the waterrepellent membrane of Experimental example 1 was cut into 25 mm×25 mm,and was used as a water repellent membrane.

<Electrolyte Solution>

A solution obtained by dissolving ammonium chloride and polyoxyethylenehaving an average molecular weight of 7,00,000 in a mixed solvent ofwater and glycerol (glycerol: 10% by mass) was used as an electrolytesolution. The ammonium chloride was 20% by mass, and the polyoxyethylenewas 8% by mass in the electrolyte solution.

<Cell Assembly>

Two barrier films were prepared by cutting a barrier film that was thesame as that of Experimental example 1 into 25 mm×25 mm, and were usedas outer case members. Nine air holes, each having a diameter of about0.2 mm, were formed in a first outer case member that was to be locatedproximately to the positive electrode. The air holes were arranged in amatrix of three columns and three rows and were spaced at regularintervals (i.e., the center-to-center distance of adjacent air holes was5 mm in both vertical and horizontal directions).

In a second outer case member that was to be located proximately to thenegative electrode, a modified polyolefin ionomer film was attached inparallel with the side of the outer case member to a portion where theexternal terminals of the positive electrode and the negative electrodewere to be arranged, in order to improve the sealing properties of thethermally welded portion between the external terminals and the outercase member.

The first outer case member proximate to the positive electrode, thewater repellent membrane, the positive electrode, the separator, and thenegative electrode were stacked in this order. Moreover, the secondouter case member was stacked thereon such that the modified polyolefinionomer film was positioned on leads of the positive electrode and thenegative electrode. Three sides of the two outer case members alongtheir peripheries were thermally welded together in a state whereperipheries of the water repellent membrane and the separator wereinterposed between the peripheries of the outer case members, and thus abag-like outer case was formed. Next after the electrolyte solution wasinjected through an opening of the outer case, the opening was thermallywelded to seal the outer case, and consequently a sheet-type air cellwas produced.

Comparative Example

<Separator>

A graft film (thickness: 30 μm) was disposed on one side of a cellophanefilm (thickness: 20 μm). The resulting film (size: 18 mm×18 mm, totalthickness: 50 μm) was used as a separator. In this case, the graft filmwas composed of a graft copolymer obtained by graft copolymerization ofacrylic acid with a polyethylene main chain.

<Water Repellent Membrane>

A polyethylene porous film that was the same as that of the waterrepellent membrane of Experimental example 1 was cut into 18 mm×18 mm,and was used as a water repellent membrane.

<Cell Assembly>

Two barrier films were prepared by cutting a barrier film that was thesame as that of Experimental example 1 into 25 mm×25 mm, and were usedas outer case members. Nine air holes, each having a diameter of about0.2 mm, were formed in a first outer case member that was to be locatedproximately to a positive electrode. The air holes were arranged in amatrix of three columns and three rows and were spaced at regularintervals (i.e., the center-to-center distance of adjacent air holes was5 mm in both vertical and horizontal directions). Then, the waterrepellent membrane was thermally welded to the inner surface of thisouter case member with a hot-melt adhesive.

In a second outer case member that was to be located proximately to anegative electrode, a modified polyolefin ionomer film was attached inparallel with the side of the outer case member to a portion where theexternal terminals of the positive electrode and the negative electrodewere to be arranged, in order to improve the sealing properties of thethermally welded portion between the external terminals and the outercase member.

The positive electrode and the negative electrode were the same as thoseof the example. The positive electrode, the separator, and the negativeelectrode were stacked in this order on the water repellent membrane ofthe outer case member proximate to the positive electrode. Moreover, thesecond outer case member was stacked thereon such that the modifiedpolyolefin ionomer film was positioned on leads of the positiveelectrode and the negative electrode. Next, three sides of the two outercase members along their peripheries were thermally welded to each otherdirectly without the water repellent membrane and the separator beinginterposed between the peripheries of the outer case members, and thus abag-like outer case was formed. After an electrolyte solution that wasthe same as that of the example was injected through an opening of theouter case, the opening was thermally welded to seal the outer case, andconsequently a sheet-type air cell was produced.

The cell of the example and that of the comparative example wereconnected to a discharge resistance of 3.9 kΩ, and were discharged. Thedischarge capacity was measured until the cell voltage was reduced to0.9 V. Table 2 indicates the measurement results.

TABLE 2 Discharge capacity (mAh) Example 46 Comparative 44 example

As indicated in Table 2, the cell of the example had dischargecharacteristics similar to those of the cell of the comparative examplein which a laminated film of the conventional cellophane film and thegraft film was used as a separator and the peripheries of the two outercase members were thermally welded to each other directly to seal thecell.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limiting. The scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges that come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

INDUSTRIAL APPLICABILITY

The sheet-type cell of this application can be used in applications thatuse a variety of cells conventionally known, and can be used as a powersupply for various devices.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1, 100 Sheet-type cell (air cell)    -   10, 110 Positive electrode (air electrode)    -   11, 111 Terminal of positive electrode    -   20, 120 Negative electrode    -   21, 121 Terminal of negative electrode    -   30, 130 Separator    -   40, 140 Water repellent membrane    -   50, 150 Outer case    -   51, 151 Outer case member proximate to positive electrode    -   52, 152 Outer case member proximate to negative electrode    -   53, 153 Air hole

1. A sheet-type cell, comprising: an outer case having a thermallyfusible resin layer, the outer case comprising: a first outer casemember; and a second outer case member; and a power generation elementprovided between the first outer case member and the second outer casemember, the power generation element comprising: a positive electrodeproximate to the first outer case member; a negative electrode proximateto the second outer case member; a separator constituted by a porousresin sheet between the positive electrode and the negative electrode;and an electrolyte solution, wherein the outer case is sealed with aperiphery of the separator interposed between a periphery of the firstouter case member and a periphery of the second outer case member. 2.The sheet-type cell according to claim 1, further comprising: a waterrepellent membrane between the first outer case member and the positiveelectrode, wherein the outer case is sealed with the periphery of theseparator and a periphery of the water repellent membrane interposedbetween the peripheries of the first and second outer case members. 3.The sheet-type cell according to claim 2, wherein the water repellentmembrane includes a porous layer made of a resin that fuses at atemperature of 200° C. or less.
 4. The sheet-type cell according toclaim 3, wherein the porous layer is made of a polyolefin.
 5. Thesheet-type cell according to claim 2, wherein the water repellentmembrane has an air permeability of 20 sec/100 ml or more.
 6. Thesheet-type cell according to claim 1, wherein the porous resin sheet ismade of a resin that fuses at a temperature of 200° C. or less.
 7. Thesheet-type cell according to claim 1, wherein the porous resin sheet isconstituted by a polyolefin porous film or a polyolefin nonwoven fabric.8. The sheet-type cell according to claim 1, wherein the separator hasan air permeability of 10 to 3000 sec/100 ml.
 9. The sheet-type cellaccording to claim 1, wherein the thermally fusible resin layer isdisposed on an inner surface of the outer case.
 10. The sheet-type cellaccording to claim 1, wherein the thermally fusible resin layer is madeof a resin that fuses at a temperature of 200° C. or less.
 11. Thesheet-type cell according to claim 10, wherein the resin that fuses at atemperature of 200° C. or less is a polyolefin.
 12. The sheet-type cellaccording to claim 1, wherein the thermally fusible resin layer isstacked on a resin layer that is to be a base.
 13. The sheet-type cellaccording to claim 1, wherein the outer case member further includes anelectrically insulating oxide layer.
 14. A method for manufacturing asheet-type cell, the sheet-type cell, comprising: an outer case having athermally fusible resin layer, the outer case comprising: a first outercase member; and a second outer case member; and a power generationelement contained in the outer case, wherein the power generationelement comprises a positive electrode proximate to the first outer casemember, a negative electrode proximate to the second outer case member,a separator between the positive electrode and the negative electrode,and an electrolyte solution, the separator is constituted by a porousresin sheet, the method comprising: stacking the first outer casemember, the positive electrode, the separator, the negative electrodeand the second outer case member; and thermally welding a periphery ofthe first outer case member and a periphery of the second outer casemember in a state where an outer portion of the separator facing neitherthe positive electrode nor the negative electrode is interposed betweenthe periphery of the first outer case member and the periphery of thesecond outer case member.
 15. A method for manufacturing a sheet-typecell, the sheet-type cell, comprising: an outer case having a thermallyfusible resin layer, the outer case comprising: a first outer casemember; and a second outer case member; and a power generation elementand a water repellent membrane that are contained in the outer case,wherein the power generation element comprises a positive electrodeproximate to the first outer case member, a negative electrode proximateto the second outer case member, a separator between the positiveelectrode and the negative electrode, and an electrolyte solution, thewater repellent membrane is disposed between the outer case and thepositive electrode, the separator is constituted by a porous resinsheet, the method comprising: stacking the first outer case member, thewater repellent membrane, the positive electrode, the separator, thenegative electrode and the second outer case member; and thermallywelding a periphery of the first outer case member and a periphery ofthe second outer case member in a state where an outer portion of thewater repellent membrane not facing the positive electrode and an outerportion of the separator facing neither the positive electrode nor thenegative electrode are interposed between the periphery of the firstouter case member and the periphery of the second outer case member. 16.The method according to claim 15, wherein the water repellent membraneincludes a porous layer made of a resin that fuses at a temperature of200° C. or less.
 17. The method according to claim 14, wherein theporous resin sheet is made of a resin that fuses at a temperature of200° C. or less.
 18. The method according to claim 15, wherein theporous resin sheet is made of a resin that fuses at a temperature of200° C. or less.